The present invention relates to techniques for extending the tuning range of a voltage-controlled oscillator (VCO) using parasitic capacitance of semiconductor devices in the VCO circuit.
Modern phase-locked loops (PLLs) used for communications need to cover wide frequency ranges while maintaining phase noise performance. Enlarging the tuning range using conventional techniques typically causes deterioration of the circuit quality factor, leading to a deterioration in the phase noise performance. Likewise, some conventional techniques, such as banded design and adding switchable varactors, may degrade the maximum operational frequency and still produce some degradation in phase noise.
Accordingly, a need arises for techniques for extending the tuning range of a VCO that does not degrade VCO circuit performance.